The field of the invention pertains to machine tools for metal cutting and metal grinding and, in particular, to coolant fluids which pour over and substantially flood the workpiece and cutting tool or grinding wheel for a variety of purposes. The foremost purpose is usually to cool the workpiece and cutting tool or grinding wheel continuously to maintain them always below a temperature that would damage the workpiece, cutting tool or grinding wheel. Other purposes are to provide a lubricating function at the interface between a cutting tool, chip and workpiece and to clean and flood away cutting debris. Cutting and grinding fluids are usually water based because they are extremely effective and inexpensive for heat removal. Unfortunately water is a relatively poor lubricant or cleaning fluid, therefore additives, chiefly soaps, have been added to provide an enhanced cleaning effect and some lubrication.
A new metal cutting fluid additive to a water coolant comprises a combination of vegetable oil such as soybean oil and a surfactant. The ratio of soybean oil to surfactant is adjusted for the machining operation to be cooled. A higher proportion of soybean oil to surfactant is preferred for metal cutting, a lower proportion of soybean oil to surfactant is preferred for metal grinding. By incorporating a biodegradable surfactant the additive is completely biodegradable thus forming a non-hazardous waste product after filtering out metal chips or grinding debris. A small amount of bacteriocide may be added to retard spoilage (rancidity) of the additive during storage or extensive re-use. The new additive is suitable for a wide variety of metals, metal alloys and other materials but also has the added benefit of protecting against corrosion of freshly machined surfaces on some common metals such as cast iron and low carbon steel.